Gas stream silencer

ABSTRACT

Noise and noise potential in a gas stream are controlled by series step treatment, each step accomplishing diffusion and smoothing of the flow with overall absorption of sound. The first stage provides a sturdy shock absorbing cushion to receive and mitigate rough blast while subsequent stages successively moderate and smooth the flow of the gas stream and absorb sound energy. Design criteria maximize diffusion and sound absorption while avoiding the creation of secondary noises within the unit.

United States Patent [191 Halter et a1.

[ GAS STREAM SILENCER [75] Inventors: Edmund John Halter; John CharlesLanpher, both of Irving, Tex.

[73] Assignee: Burgess Industries Incorporated,

Dallas, Tex.

[22] Filed: Aug. 20, 1974 [21] App]. No: 498,984

[52] [1.8. CI i. 181/50; 181/57 [51] Int. Cl. t l t ..F01n 1/10 [58]Field of Search 181/49 50, 53, 57, 58

[56] References Cited UNITED STATES PATENTS 759964 5/1904 Bonar i i l181/57 992.839 5/1911 Wolle et al. 181/57 X 2.640.557 6/1953 Gaffney l ll i i i i l 181/50 2.764250 9/1956 Jeffords 181/50 [451 July 15, 19751196,977 7/1965 Sanders 181/50 Primary ExaminerJoseph W. HartaryAssistant Examiner-.lohn F. Gonzales Attorney, Agenl, or FirmDarbo,Robertson &

Vandenburgh [57] ABSTRACT Noise and noise potential in a gas stream arecon' trolled by series step treatment, each step accomplishing diffusionand smoothing of the flow with overall absorption of sound. The firststage provides a sturdy shock absorbing cushion to receive and mitigaterough blast while subsequent stages successively moderate and smooth theflow of the gas stream and absorb sound energy. Design criteria maximizediffusion and sound absorption while avoiding the creation of secondarynoises within the unit.

10 Claims, 9 Drawing Figures FMEWEUJUL 1 5 ms SHEEI 1 GAS STREAMSILENCER BACKGROUND AND SUMMARY OF THE INVENTION The history of noisecontrol has been a story of stepby-step technological improvement withconcurrent progressive realization of the physiological, psychologicaland sociological importance of minimizing the levels of noise to whichpeople are exposed. The scientific principles involved in the art aredrawn and combined from the fields of acoustics, pneumatics andhydraulics. As in the mechanical arts, known physical expedients arecombined in new relationships with dimensional and other design criteriadiscovered to provide the ever sought improved results.

In the particular field of the treatment and control of gas streams,especially pulsating or pressure and/or velocity disordered flow, it isnecessary to deal with complicated problems of eliminating or at leastgreatly attenuating sonic frequency systems as well as smoothing andotherwise altering the flow to avoid the generation of noise directlyupon discharge to the atmosphere or indirectly by causing noise creatingvibrations of mechanical apparatus. At the same time, the production ofsecondary noise in the silencer, itself, or other treating device mustbe avoided.

The object of the present invention is to provide a silencer forcontrolling the noise. existing or potential, of a gas stream and whichis capable of absorbing noise created upstream and smoothing disorderedflow to avoid the creation of noise downstream while avoiding thecreation of secondary noise within the silencer, it self. The device iscapable of handling streams having a wide range of pressure and velocityflow characteristics, including surges of blast proportions.

A further object is to provide such a silencer which has a long anddependable useful life. Another object is to provide such a plural stagesilencer to which an additional stage or stages may be added to providemore complete silencing as noise pollution standards become more strict.Another object is to provide such a silencer which has a very highperformance/size ratio.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a typical silencerof the invention.

FIG. 2 is a longitudinal view, in cross section, of the silencer of FIG.1.

FIG. 3 is an enlarged detail view showing structure and indicatingaction in the shock absorbing section of the unit.

FIGS. 3A and 3B are detail views showing the perforation patterns of theinner shells and of the diffusers, respectively, full size.

FIGS. 4 and 5 are detail views in cross section showing alternativeforms of vibration isolating connection of adjacent sections of thesilencer, the structure of FIGS. 1 and 2 being that illustrated in FIG.4.

FIG. 6 is an exploded view of an add-on unit.

FIG. 7 is a side view of a modified form of a silencer.

DESCRIPTION OF SPECIFIC EMBODIMENTS The silencer illustrated in FIGS.1-4 is a two-section unit comprised of cylindrical shells I and 2, theinlet end being closed by head 3. First stage diffuser tube 4 is weldedto the head structure and a standard connecting flange 5 is welded tothe exposed inlet end of the diffuser tube. The cylindrical walls of thetube are perforated, the pattern being shown, full size, in FIG. 38. Anorifice plate 6 having an orifice 7, the purpose of which will bedescribed hereinafter, is shown lying against the face of flange 5.

The contiguous ends of shells l and 2 are provided with flanges 8 and 9.A partition I0 having a central opening II and a peripheral flange 12 ismounted at the junction of the first and second stages of the silencerby means of the peripheral flange. Elastomeric spacers I3 are sandwichedbetween flange I2 and flanges 8 and 9 before the joint is drawn up tightby bolts [4, the function of the elastomeric spacers being to preventthe transmission of vibration between the shells connected at the joint.

Inner cylindrical shells I5 and I6 are mounted by means of rings 17 inspaced relation to shells I and 2. The inner shells are perforated, asshown. to provide access from the interior of the silencer to thematerial packed into the spaces between the inner shells and thesilencer shells. The nature and function of these materials will bedescribed hereinafter. The perforation pattern of the inner shells isshown, full size. in FIG. 3A.

A second stage diffuser tube I8 is mounted in opening II of partitionI0. This tube, like the first stage diffuser tube, is perforated, asshown.

Desirably, a perforated inner head 19 is mounted in spaced relation tohead 3 and the space thus provided is filled with sound absorbingmaterial such as a pack of copper or steel fibers. Also, shell I of thefirst section of the silencer is double wrapped with a shell vibrationdampening material such as lead or asbestos sheet 21. A sheet metalcovering is provided.

While the gas stream silencer of the invention may be connected inline;" that is, connected at its inlet end to receive gases from aconduit and connected, also, at its outlet end with a conduit, thedevice shown in the drawing is designed to terminate the gas flowconduit. The inner and outer shells at the outlet end 22 of the silencerare open to the atmosphere.

The gas stream, the characteristics of which may vary from a relativelysmooth flow to violently pulsating flow, is directed into first stagediffuser tube 4. Since the downstream end of the tube is closed, thegases are forced to flow radially outwardly through the tubeperforations. For the duration of each pulse, the gases are directed ina multiplicity of individual jets toward inner shell IS. The space 23surrounding the diffuser tube is filled with a durable type of material,such as metal turnings or copper scrubble, which provides a body havinginterconnecting voids. While serving to contribute to the absorption ofsound vibrations in the gases from upstream sources, the principalfunction of this body is to receive and cushion the impact of the jetstreams issuing from diffuser tube 4. Otherwise stated, while soundabsorption is a desired characteristic of the material contained inspace 23, this characteristic is somewhat sacrificed to achieveresistance to disintegration by the gases flowing at high velocitythrough the perforations of inner shell 15 and into the voids in thebody. The space 24, which is downstream from the diffuser but still apart of the first, shock section of the silencer, is preferably filledwith the durable type of sound absorbing material. Sound energy isabsorbed by the material in spaces 23 and 24 and also by the soundabsorbing material 20 which is also exposed to the space within thefirst stage of the silencer.

The accomplishment of the flow treatment in the first section of thesilencer is a partial but substantial smoothing of the flow of the gasesfollowing exposure to the shock and sound absorbing bodies.

The second stage of the silencer is designed to further damp pulsationsand absorb sound energy still existing in the stream of gases as itfiows from treatment in the first stage into the second stage diffusertube I8. While treatment action in the second stage is similar in natureto that brought to bear in the first stage of the silencer, the emphasisis changed from mitigation of shock flow to sound absorption withcontinued smoothing of the flow to prepare the stream for emission tothe atmosphere with minimum noise-creating impact. Sound energy isabsorbed by a more efficient sound absorbing material than thatcontained in the first section, such as punched hairfelt or glass fiber.contained in the spaces 25. Noise having their sources upstream from thesilencer and noise that may be created in the gas system within thesilencer are absorbed to an acceptable level before reaching the outletof the silencer.

The gas stream silencer must be designed, not only to absorb so far aspossible noise energy reaching it from upstream sources and smooth theflow to avoid the creation of noise at or beyond the outlet of thesilencer, but also to avoid the creation of noise within the silenceritself. The generation of low frequency flow noise which tends to occurwhen a relatively high velocity stream flows into a large volume, suchas emission of a stream from an inlet conduit into a relatively largesilencer chamber, is avoided in the silencer herein described. The inletstream is divided into a multiplicity ofjets 26 (FIG. 3) and the shockabsorbing material is .arranged somewhat beyond the jet cores asrepresented at 27 in the enlarged detail view of FIG. 3. The preferreddistance between inlet tube 4 and perforated inner shell is from four totimes the diameter of the perforations in the diffuser tube. With thisconfiguration. damage to the shock absorbing material by the highvelocity jet cores is avoided and the gases are received and treatedwithout the generation of low frequency noise. This distance may besomewhat less or may be greater with some sacrifice of useful life ofthe shock absorbing material or acoustic performance of the silencer,but the dimension specified represents optimum design.

Following treatment of the gas stream in the first, shock, stage of thesilencer, the gases flow into the second stage diffuser tube 18 andradially therefrom through the perforations therein. Preferably, theperforations in the second stage diffuser tube are somewhat smaller andthe tube somewhat longer as compared with the corresponding dimensionsof the first stage diffuser. This results in smaller and more numerousjets. While the second stage diffuser tube effects further smoothing ofthe flow, the primary emphasis in the second treatment stage isacoustical; that is, the absorption of sound waves traveling in the gasstream. The spaces are packed with an efficient sound absorbingmaterial, such as hairfelt or glass fiber. As is shown in FIG. 1, theexposed area of the sound absorbing material is extended well beyond theclosed downstream end of the diffuser tube to provide continuedabsorption of sound energy as the stream consolidates for exit to theatmosphere at relatively low and steady velocity through the opendownstream end of the silencer.

The silencer must necessarily be designed to handle a predeterminedmaximum flow of gases. While a valve in the upstream conduit leading tothe silencer may be provided to limit the flow, secondary noises arelikely to be generated downstream from the valve. This can be avoided byemploying an orifice plate 6 at the inlet to the first stage diffusertube. The amount of open area provided by the totality of perforationsin the diffuser tube is related to the size of orifice 7. In general,this area should be approximately three times the area of the orifice.If, as is preferred, the perforations in the second stage diffuser tubeare somewhat smaller than those in the first diffuser tube, the totalopen area for flow through the perforations in the second tube may beapproximately the same as that of the first tube for optimum resultssince the flow of the stream into the second diffuser tube issubstantially smoother.

Normally, it is necessary to provide means for preventing the radiationof noise to the atmosphere from the shell of the first or shock stage,only, of a two-stage silencer. This is done by surrounding the shell 1with vibration damping layers, as above described. Transmission of thevibration of the first stage shell I to shell 2 of the second stage islargely avoided by the interposition of the elastomeric material at thejoint as above described and the relatively smoother flow of the gasstream into and through the second stage does not normally createtroublesome vibration of the shell.

An alternative form of vibration isolating joint is shown in FIG. 5. Inthis arrangement, the ends of shells la and 2a overlap and are fastenedtogether with an elastomeric spacer 13a sandwiched between as avibration barrier.

Although it is generally more desirable from both cost and performanceefficiency standpoints to construct the silencer with cylindricalshells, they may, alternatively, be conical as shown in FIG. 7. Designconsiderations described with reference to the silencer of FIGS. 1-4 areapplicable to the unit shown in FIG. 7 which differs essentially only inthat the shells are conical instead of cylindrical.

The trend over the years has been to require better and better silencingto reduce noise pollution. What is acceptable and tolerated today isinadequate to meet the more stringent standards of tomorrow. Inrecognition of this trend and the likelihood that it will continue inthe future, the invention contemplates the possible future addition ofone or more gas stream treatment stages to the initially installedsilencer which may comprise only two stages. This concept is illustratedin FIG. 6 wherein the initial two-stage unit is provided with aconnecting flange 28. An add-on" stage 29, comprising shell 30 having alining of sound absorbing material 31, diffuser tube 32 and connectingelements, is shown in position for connection to the outlet end of theinitial two-stage unit. If desired at a later date, an additional stageor stages may be inserted between the initial unit and the terminalstage 29.

The silencer shown in FIG. 6 illustrates a further alternative featureof construction. To still further enhance the quieting of the gasstream, a sound absorbing body 33, contained between inner solid tube 34and outer perforated tube 35 is provided as an extension of diffusertube 32. Extended sound absorption is effected by passage of the streamthrough the annular passageway defined by the sound absorbing bodysurfaces.

The silencer of this invention is very flexible in its usefulapplications. While the taming of relatively violent flow is its forte,it is effective in pressure reduction applications, such as the quietexhausting of steam under pressure to the atmosphere.

We claim:

1. In a plural stage gas stream silencer having circular shell meansdefining a plurality of treatment sections connected in series for theflow of a gas stream there through, each section having a central inletopening therein and at least the side walls of the shell means havingtheir internal surfaces covered with a layer of sound absorbing materialheld in position by perforated inner shell means; the improvementwherein a diffuser tube is mounted in each inlet opening and extendsdownstream therefrom into but not through the associated treatmentsection; each said tube being open at its upstream end, closed at itsdownstream end and having its side walls perforated; the distance fromsaid perforated side walls to the perforated inner shell meanssurrounding the same being greater than four times the diameter of theperforations in said side walls; the sound absorbing material of thelayer surrounding said diffuser in the treatment section at the inletend of the silencer consisting of a durable material such as metalturnings; the layer of sound absorbing material of succeeding treatmentsections comprising material having high sound absorption capabilitysuch as punched hairfelt or glass fiber.

2. Structure in accordance with claim 1 wherein the distance from theperforated side walls to the perforated inner shell means surroundingthe same is from four to twenty times the diameter of the perforation insaid side walls.

3. Structure in accordance with claim 1 and including a layer ofvibration damping material surrounding the shell means defining thetreatment section at the inlet end of the silencer to minimize theradiation of noise from said shell means to the atmosphere.

4. Structure in accordance with claim 1 wherein the shell means definingadjacent sections are connected together with resilient materialsandwiched between and separating contiguous shell means structurewhereby to minimize the transmission of vibration from the shell meansof one section to the shell means of the adjacent section.

5. Structure in accordance with claim 4 wherein the joints connectingadjoining treatment sections comprise flanges mounted upon therespective shell means. a layer of resilient material arranged betweensaid flanges. and fastening means drawing and holding the flangestogether with said layer sandwiched therebetween.

6. Structure in accordance with claim 4 wherein the joint connectingadjoining treatment sections comprise spaced telescoping end portions ofthe shell means and a layer of resilient material filling the spacebetween said telescoping end portions. and means fastening saidtelescoping end portions together with said resilient materialsandwiched therebetween.

7. Structure in accordance with claim 1 wherein the outlet end of thefinal treatment section of the silencer is provided with means forconnection thereto of an additional treatment section whereby the degreeoftreatment of the gas stream may be increased at some time after theinitial installation and use of the silencer.

8. Structure in accordance with claim I and including a downstreamextension of a diffuser tube. said extension having a layer of soundabsorbing material exposed to the gas stream and defining with the innershell an annular passageway for the gas stream.

9. Structure in accordance with claim 8 wherein the extension of thediffuser tube in in the final treatment section of the silencer.

10. Structure in accordance with claim 1 wherein the shell means inconical, the small end being the inlet end of the silencer and the largeend being open to the atmosphere.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO.3,894,610

DATED July 15, 1975 INVENTOWS) i Edmund John Halter; John CharlesLanpher It rs certrfred that error appears rn the ahove rdentrfiedpatent and that said Letters Patent are hereby corrected as shown below:

Col. 3 line 38 6 line 15 6 line 33 line 36 C01. C01. C01. 6

[SEAL] Attest.

RUTH C. MASON Arresting Officer Signed and Scaled this fourzeentir DayOf October 1975 C. MARSHALL DANN Commissioner nfPaIenls and Trademarks

1. In a plural stage gas stream silencer having circular shell meansdefining a plurality of treatment sections connected in series for theflow of a gas stream therethrough, each section having a central inletopening therein and at least the side walls of the shell means havingtheir internal surfaces covered with a layer of sound absorbing materialheld in position by perforated inner shell means; the improvementwherein a diffuser tube is mounted in each inlet opening and extendsdownstream therefrom into but not through the associated treatmentsection; each said tube being open at its upstream end, closed at itsdownstream end and having its side walls perforated; the distance fromsaid perforated side walls to the perforated inner shell meanssurrounding the same being greateR than four times the diameter of theperforations in said side walls; the sound absorbing material of thelayer surrounding said diffuser in the treatment section at the inletend of the silencer consisting of a durable material such as metalturnings; the layer of sound absorbing material of succeeding treatmentsections comprising material having high sound absorption capabilitysuch as punched hairfelt or glass fiber.
 2. Structure in accordance withclaim 1 wherein the distance from the perforated side walls to theperforated inner shell means surrounding the same is from four to twentytimes the diameter of the perforation in said side walls.
 3. Structurein accordance with claim 1 and including a layer of vibration dampingmaterial surrounding the shell means defining the treatment section atthe inlet end of the silencer to minimize the radiation of noise fromsaid shell means to the atmosphere.
 4. Structure in accordance withclaim 1 wherein the shell means defining adjacent sections are connectedtogether with resilient material sandwiched between and separatingcontiguous shell means structure whereby to minimize the transmission ofvibration from the shell means of one section to the shell means of theadjacent section.
 5. Structure in accordance with claim 4 wherein thejoints connecting adjoining treatment sections comprise flanges mountedupon the respective shell means, a layer of resilient material arrangedbetween said flanges, and fastening means drawing and holding theflanges together with said layer sandwiched therebetween.
 6. Structurein accordance with claim 4 wherein the joint connecting adjoiningtreatment sections comprise spaced telescoping end portions of the shellmeans and a layer of resilient material filling the space between saidtelescoping end portions, and means fastening said telescoping endportions together with said resilient material sandwiched therebetween.7. Structure in accordance with claim 1 wherein the outlet end of thefinal treatment section of the silencer is provided with means forconnection thereto of an additional treatment section whereby the degreeof treatment of the gas stream may be increased at some time after theinitial installation and use of the silencer.
 8. Structure in accordancewith claim 1 and including a downstream extension of a diffuser tube,said extension having a layer of sound absorbing material exposed to thegas stream and defining with the inner shell an annular passageway forthe gas stream.
 9. Structure in accordance with claim 8 wherein theextension of the diffuser tube in in the final treatment section of thesilencer.
 10. Structure in accordance with claim 1 wherein the shellmeans in conical, the small end being the inlet end of the silencer andthe large end being open to the atmosphere.